The invention relates to electrochemical cells.
A current producing electrochemical cell has to satisfy many requirements in order to be of wide ranging practical value. One such requirement is a long shelf life, that is, the cell must show a negligible rate of self-discharge. While this is quite obvious for primary cells, it is also true of secondary or rechargeable cells.
One type of modern high energy density cell makes use of alkali metal anodes, non-aqueous electrolytes, and transition metal sulfide cathodes. The latter are solid compounds which upon reduction incorporate the alkali metal without substantial structural changes. A sepecific example of this type of cell would be a Li/2MeTHF-THF-LiAsF.sub.6 /TiS.sub.2 cell, for which the reaction can be written as follows: EQU xLi+TiS.sub.2 .fwdarw.Li.sub.x TiS.sub.2 (0&lt;x&lt;1) E.about.2.1V
In the above cell the listed reactants are completely insoluble in the electrolyte, and therefore one would expect to see no self-discharge reactions and, accordingly, the cell should have a practically indefinite shelf life.
Rao et al., 128 J. Electrochem. Soc. 942 (1981), discuss how an electrochemical cell having a lithium anode, a titanium disulfide cathode, and an aprotic organic electrolyte can self-discharge if the cathode contains a sulfur impurity such as elemental sulfur or hydrogen sulfide. According to Rao et al., such impurities may be introduced as a byproduct in the production of TiS.sub.2 and through the handling of the TiS.sub.2 in a non-inert environment during cell assembly.